3GPP that is a standardization group of W-CDMA is studying a communication scheme that becomes a successor to W-CDMA and HSDPA, that is, 3GPP is studying Long Term Evolution (LTE). As radio access schemes, OFDM (Orthogonal Frequency Division Multiplexing) is being studied for downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) is being studied for uplink (refer to non-patent document 1, for example).
OFDM is a multicarrier scheme for dividing a frequency band into a plurality of narrow frequency bands (subcarriers) so as to perform transmission by carrying data on each subcarrier. By arranging the subcarriers on frequencies densely without interfering with each other while a part of them overlap, high speed transmission is realized so that efficiency of use of frequency increases.
SC-FDMA is a single carrier scheme that can decrease interference among terminals by dividing frequency band and performing transmission using frequency bands that are different among a plurality of terminals. Since the SC-FDMA has characteristics that variation of transmission power becomes small, low power consumption in the terminal and wide coverage can be realized.
By the way, in the mobile communication system, in order to improve transmission characteristics, there is a case in which receive diversity for receiving a signal using two or more antennas is applied. It is planned that the mobile station in LTE is generally provided with two antennas for applying receive diversity in order to improve transmission characteristics of the downlink. The mobile station can be called a user apparatus (UE: User Equipment) more generally. When the mobile station is provided with two antennas so that receive diversity is applied, cost and size of the mobile station become large. Thus, the receive diversity is not essential in W-CDMA.
In order to avoid that cost and size of the mobile station become large when the mobile station is provided with two antennas, there is a case in which a sensitive and high-performance antenna is provided as one of the two antennas, and a low-performance antenna which is relatively not sensitive is provided as another of the two antennas. For convenience of explanation, the former antenna is called a main antenna, and the latter is called a sub-antenna. In addition, in this case, generally, for performing uplink transmission, the former sensitive and high-performance antenna is used for transmission. That is, in the downlink, reception is performed using two antennas. In the uplink, transmission is performed using the high-performance antenna of the two antennas.
In the mobile communication system, a communication area is comprised of a plurality of cells. The mobile station performs communication in one or more cells in the plurality of cells. In LTE, since hard handover is applied, the mobile station communicates with one cell, and when a cell having better quality than the serving cell, the mobile station performs handover to the cell of the better quality.
For example, in HSDPA to which hard handover is applied like LTE, the mobile station measures any one of pilot signal received power (CPICH RSCP), ratio between pilot signal received power and total received power including noise power (CPICH Ec/N0), and path loss. When a cell having better quality than the serving cell appears, the mobile station reports the best cell to the network. This report is called measurement report (MR). The network performs processing for changing the serving cell based on the measurement report (non-patent document 2).
The path loss is defined as follows. Pathloss in dB=Primary CPICH Tx power−CPICH RSCP, wherein Primary CPICH Tx power is pilot signal transmission power in the base station apparatus, and CPICH RSCP is pilot signal received power in the mobile station. As is clear from the above equation, path loss is a value calculated automatically from the pilot signal received power (CPICH RSCP) and the pilot signal transmission power (CPICH).
The above-mentioned report on change of best cell is called event 1D (Reporting event 1D). In addition, the network specifies, to the mobile station, which one the mobile station measures among the pilot signal received power, the ratio between pilot signal received power and total received power including noise power, and the path loss. More particularly, the network uses system information in a broadcast channel or uses a measurement control message in order to specify which one the mobile station measures among various metrics such as the pilot signal received power, the ratio between pilot signal received power and total received power including noise power, and the path loss. The network is the radio network controller (RNC) in the WCDMA.
The reason for the network to specify which one the mobile station measures among the pilot signal received power, the ratio between pilot signal received power and total received power including noise power and the path loss is for designing cells more flexibly. For example, when there are two network operators, one network operator can specify path loss to the mobile station, and another network operator can specify pilot signal received power. Alternatively, one network operator can specify path loss to the mobile station in a suburban area, and the network operator can specify pilot signal received power in an urban area.
When a mobile station that has two antennas for which receive diversity is applied performs the measurement report, it is necessary to calculate the pilot signal received power (CPICH RSCP), and the ratio between pilot signal received power and total received power including noise power (CPICH Ec/N0) in consideration of the two antennas. For example, as methods for calculating the pilot signal received power (CPICH RSCP), and the ratio between pilot signal received power and total received power including noise power (CPICH Ec/N0) for the mobile station for which receive diversity is applied, following three methods are proposed (refer to non-patent document 3, for example).
[1] Either one of the antennas is defined as a main antenna, and each of CPICH RSCP and CPICH Ec/N0 is a value measured by the main single antenna.
[2] Each of CPICH RSCP and CPICH Ec/N0 is an average value of values measured by two antennas.
[3] Each of CPICH RSCP and CPICH Ec/N0 is a sum value of values measured by two antennas.
In addition, in the three methods, the non-patent document 4 proposes the third method in which the total value of the values measured by two antennas is used.
[Non-patent document 1] 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006
[Non-patent document 2] 25.331 V6.11.0 2006-09
[Non-patent document 3] Nokia, R4-061294, “RRM measurements on a WCDMA UE with multiple antenna connectors”, November, 2006
[Non-patent document 4] Nokia, Qualcomm, R4-070238,
“Further discussion on RRM measurements on a WCDMA UE with multiple antenna connectors”, February, 2007